Audible explosive device simulator system for miles

ABSTRACT

An acoustic training device for simulating the effects of a weapon posing  omnidirectional threat in a tactical engagement simulation system generates an audible signal of a predetermined frequency and duration once activated. The amplitude of the signal generated corresponds to the kill-zone of the weapon being simulated. The signal may be modulated so as to produce a predetermined number of pulses which are easily distinguished from other noises associated with the tactical exercise.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured, used and licensed byor for the U.S. Government for Governmental purposes without payment tous of any royalty thereon.

This is a continuation-in-part of application Ser. No. 07/691,603, filedApr. 18, 1991, now U.S. Pat. No. 5,199,874.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to Multiple Integrated LaserEngagement System (MILES) type training devices and more particularly toan acoustic training device for simulating the effects of a weaponposing an omnidirectional threat in a tactical engagement simulationsystem such as the MILES.

2. Description of the Prior Art

The Multiple Integrated Laser Engagement System ("MILES") hasrevolutionized the way in which armies train for combat. MILES has beenfielded with armies of many nations around the world and has become theinternational standard against which all other Tactical EngagementSimulation ("TES") systems are measured. For the U.S. Army and MarineCorps, MILES is the keystone for their opposing force, free-lay TESProgram. It is highly valued in its ability to accurately assess battleoutcomes and to teach soldiers the skills required to survive in combatand destroy the enemy.

With MILES, commanders at all levels can conduct opposing forcefree-play tactical engagement simulation training exercises whichduplicate the lethality and stress of actual combat.

The MILES system uses laser bullets to simulate the lethality andrealism of the modern tactical battlefield. Eye-safe Gallium Arsenide(GaAs) laser transmitters, capable of shooting pulses of coded infraredenergy, simulate the effects of live ammunition. The transmitters areeasily attached to and removed from all hand-carried and vehicle mounteddirect fire weapons. Detectors located on opposing force troops andvehicles receive the coded laser pulses. MILES decoders then determinewhether the target was hit by a weapon which could cause damage(hierarchy of weapons effects) and whether the laser bullet was accurateenough to cause a casualty. The target vehicles or troops are madeinstantly aware of the accuracy of the shot by means of audio alarms andvisual displays, which can indicate either a hit or a near miss.

The coded infrared energy is received by silicon detectors located onthe target. In the case of ground troops, the detectors are installed onwebbing material which resembles the standard-issue load-carrying liftharness. Additional detectors are attached to a web band which fits onstandard-issue helmets. For vehicles, the detectors are mounted on beltswhich easily attach to the front, rear, and sides. The detectors provide360 degree coverage in azimuth and sufficient elevation coverage toreceive the infrared energy during an air attack. The arriving pulsesare sensed by detectors, amplified, and then compared to a thresholdlevel. If the pulses exceed the threshold, a single bit is registered inthe detection logic. Once a proper arrangement of bits exists,corresponding to a valid code for a particular weapon, the decoderdecides whether the code is a near miss or a hit. If a hit isregistered, a hierarchy decision is then made to determine if this typeof weapon can indeed cause a kill against this particular target and, ifso, what the probability of the kill might be.

While great success has been enjoyed with weapons that can be aimedthere has been no convenient or economic way for the military to trainwith grenades that interact with the MILES system. This is because agrenade rotates during its ballistic flight path and would requireseveral laser emitters so that at least one would be pointed at atarget. However, even a large number of emitters would not assure a hit.Due to these difficulties, no grenade exists that interacts with thepresent MILES system. Consequently, there is a great need to find a wayin which grenades and other ballistic or variable-directional flightpath type weapons can be used in training exercises with MILES.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anacoustic indirect-fire training device for use in a tactical engagementsimulating system which is responsive to acoustic signals.

It is another object of the present invention to provide an acousticindirect-fire training device which emits an acoustic signal ofsufficient intensity to indicate a hit in a tactical engagement systemwithin a "kill zone" approximating that of the actual weapon beingsimulated.

It is still another object of the invention to provide an acousticindirect-fire training device which emits an acoustic signal which iseasily distinguished by a tactical engagement systems from otherbattlefield and ambient noises.

It is yet another object of the present invention is to provide anacoustic indirect-fire training device which resembles actual weaponryin appearance and use, but which can be thrown or otherwise used incombat simulation without causing injury to the players, and which canbe immediately reused.

Another object of the present invention is to provide an acousticindirect-fire training device which furnishes an intense visual signalto the players along with an acoustic signal.

The present invention achieves these objectives by using a predeterminedacoustic signal to simulate an explosion in combination with receivercircuitry sensitive to the acoustic signal and operatively connected tothe existing MILES power supply. A special feature presentlyincorporated in the MILES provides for an audible alarm to be activatedupon removal and reinsertion of the MILES power source. This featureprevents someone from cheating by deactivating his MILES receiver duringsimulated combat. When the power source (typically a battery) isreinstalled an audible alarm is sounded. Consequently, by momentarilyremoving the MILES power source from the circuit for a brief instant andthen reconnecting it back into the circuit the present invention is ableto indicate a kill on MILES. This operation is performed when receivercircuitry detects a predetermined acoustic signal of sufficientamplitude and duration or can even be a coded acoustic signal. Anacoustic signal overcomes the disadvantage of highly directional laserpulses because of its substantially omnidirectional propagationcharacteristics.

Consequently, a grenade, or other variable-directional explosive typedevice, that incorporates a sonic device or buzzer will be able tointeract with the MILES that have been fitted with the presentinvention. The use of a pull pin and switch arrangement providessoldiers with a realistic grenade fop use in training operations. Anoptional "safety" lever pivotally attached to the grenade can be used tohold the switch open and provide realistic operation. A grenade thatgenerates an audible signal is described in a copending applicationserial number: 07/008,923, entitled "TRAINING GRENADE" and is assignedto same assignee, the U.S. Government, as in this case.

The acoustic signal generated by the grenade is detected by receivercircuitry located and operatively connected to the power supply sourcefor the MILES. The operational sequence of the simulator system is asfollows. When a grenade is activated there is approximately a threesecond delay before a flash bulb fires. A flash may be used to provide avisual means for indicating that an explosion has occurred but, it isnot essential. A delay is also advantageous so that the thrower does notactivate his own received circuitry. After the flash fires a buzzersounds for approximately three seconds. Obviously, other time periodsmay be selected. A means for detecting the acoustic signal, for examplea microphone, is located on each target which has been fitted with aMILES. Targets can be vehicles, soldiers, buildings, etc. The microphonethat detects the sound generated by the grenade is connected to receiverand identification circuitry. The output of the receiver is used as atrigger signal to momentarily remove the MILES power source from therest of the MILES circuit. This results in the MILES audible alarm beingactivated.

The present invention is not limited to using a grenade. Varioustraining devices, particularly ones that have variable-directionalflight paths, can be designed to generate a predetermined audible signalsimulative of an explosion. However, the present disclosure willprimarily be directed towards the use of an audible grenade and itsinteraction with the simulator receiver circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, uses and advantages of thepresent invention will be mope fully appreciated as the same becomesbetter understood when considered in connection with the followingdetailed description of the present invention and in conjunction withthe accompanying drawings, in which:

FIG. 1 shows a cross sectional view of a training grenade that can beused to generate an acoustic signal according to an aspect of theinvention.

FIG. 2 shows an electrical schematic diagram of a training grenade asdepicted in FIG. 1.

FIG. 2a shows an electrical schematic diagram of an acousticallymodulated training grenade as depicted in FIG. 1.

FIG. 3 shows an electrical schematic diagram of a basic embodiment ofthe receiver circuitry according to an aspect of the invention.

FIG. 4 shows a partial electrical schematic diagram of decodingcircuitry as added to the circuitry as shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, like reference numerals representidentical or corresponding parts throughout the several views. Before adescription is given on the receiver circuitry a description of anaudible grenade of the type that can be used in the present inventionwill be described.

A cross sectional view of a grenade 100, having a barrel shape as usedin many fragmentation grenades, is shown in FIG. 1. The housing 102 maybe made from a transparent or translucent, synthetic, flexible or shockresistant material.

The housing material should be chosen so as to lessen the possibility ofconcussion or other types of injury in cases where the grenade 100 hitsan unprotected player. A preferred material for this purpose is apolyurethane elastomer, such as that produced by the Dow ChemicalCompany of Midland, Mich., and known as Pellethane, Part No. 2103-70A.Pellethane has a Shore A durometer of 72 and a specific gravity of 1.06,making it a suitable choice for the housing 102. The grenade 100contains a power supply or standard 9 volt battery 104 to power anelectronic circuit mounted on circuit board 108 which fires a lightemitting device 108 which then triggers a buzzer 110. Obviously, thegrenade 100 need not be transparent nor translucent if a flash bulb isnot used. If a flash bulb is used it illuminates the translucent housing102 of the grenade 100. The light emitting device 108 could be, forexample, a common type camera flash bulb such as a Sylvania Blue Dot, alight emitting diode, or a xenon flash beacon. Removing the pull ring112 and safety pin 113 causes a phone type switch 114 to close, therebyproviding power to the circuit.

The electronic circuit mounted on circuit board 106 is shown inschematic form in FIG. 2 and comprises a phone type switch 114, a flashbulb 108, a bummer 110, and activation means 118. The activation means118 comprises battery 104, a timing means 118 which may comprise aresistor 120 (R1), resistor 122 (R2) and capacitor 124 (C1) network, anda Motorola MC1455 monolithic timing circuit 128. Upon removal of thesafety pin 113, by pulling on a safety pin pull ring 112, the switch114, in series combination with battery 104, closes. The removal of thesafety pin 113 starts the charging of timing means 118 within theactivation means 118. After approximately a three second delay the flashbulb 108 is fired. This causes the buzzer 110 to sound for approximatelythree seconds thereby simulating the spread of fragments.

As mentioned previously, the acoustic signal may also be modulated at apredetermined frequency to further distinguish over the backgroundnoises associated with a training exercise. Of course, the unmodulatedcarrier signal must be of sufficient amplitude to be received withoutsignificant attenuation over a distance roughly corresponding to the"kill zone" of an actual explosive device. The practical limit in termsof human hearing would be about 120 dB. For a zone corresponding to thedestructive of a conventional hand grenade, however, a signal of 75-80dB at one meter is appropriate.

A modulated signal is generally preferred for purposes of reliability,as it allows the receiver circuitry to count pulses before indicating ahit. This cuts down on false hits and adds to the realism of thetactical simulation. Even where the receiver circuitry is tuned to aparticular frequency and modulation scheme, it is sometimes possible forcertain activities, such as starting an engine, to include the very samefrequency components for a sustained period of time thereby exceedingpredetermined receiver thresholds and indicating a false hit. For thisreason, the carrier signal should be produced and modulated long enoughfor at least three pulses to be emitted. In fact, the receiver circuitrydescribed in parent application, Ser. No. 07/691,603 looks for eightsuch pulses before it indicates a hit. Thus, current designs employgreater than eight pulses, with sixteen being preferred for purposes ofreliability.

Since grenade fragments can be in transit anywhere from one to threeseconds, sixteen pulses are easily emitted with a pulse-modulation rateof 50-100 milliseconds. Carrier frequencies are determined by thefrequency of the crystal oscillator employed. A carrier frequency of3750 Hz and a pulse rate of 69 msec have been implemented successfullyand at minimum expense in connection with the receiver hereinafterdescribed.

FIG. 2a illustrates an electronic circuit 300 mounted on circuit board106 which implements a modulated acoustic signal in a grenade 100. Twoswitches 301 and 302 control grenade initiation. The start switch 301connects the battery 305 to the balance of the circuit and may beactivated by a pull-pin or some other means appropriate to the weaponbeing simulated. In the case of a grenade-like training device, thedisable switch 303 is normally closed and must be manually held open toprevent the device from being activated. In a normal training sequence,the start switch 301 is activated via the pull-pin (not shown) and thedisable switch 303 is activated shortly thereafter by releasing the pushbutton (not shown). When the disable switch 303 is activated, binarycounter 307 begins counting the clock pulses generated by the crystaloscillator 309. Binary counter 307 provides both the fundamentalfrequency (3750 Hz) for the transducer 311 and a clock frequency for thesecond binary counter 313. The second binary counter 313 provides thetone modulation frequency of 7.32 Hz, the control signal at 4.37 secondswhich turns the transducer 311 on, and the control signal at 8.74seconds which turns the transducer 311 off.

Resistor 315 and capacitor 317 filter the battery voltage and act as abuffer to isolate the timer circuit from the effect of the flashbulbload 345 on the battery 305. Resistor 319 and capacitor 321 provide ashort delay between the release of the disable switch 303 and timerinitiation. Capacitor 321 also prevents the timer 307 from being resetby the disable switch 303 once the timer 307 has started. Binary counter307, a CD4060 with oscillator, is used in conjunction with components323, 325, 327, 329, 331 and 309 to generate the fundamental (or carrier)frequency (3750 Hz) and to generate a clock signal for the secondcounter 313, a 12-stage binary counter. The second binary counter 313provides the tone modulation signal as well as the time delays to startthe tone modulation and to stop it.

NAND gate 333 "ands" the tone modulation signal with the 3750 Hz signal.NAND gate 335 "ands" the tone modulation start and stop signals with thetone modulation signal. NAND gate 337 is then used as an inverter toprovide the proper polarity signal to N-type MOSFET 339.

When the disable switch 303 is released, the timer 307 begins after ashort (approximately 5 millisecond) delay. The output of NAND gate 333begins to switch after about 68 milliseconds and continues to changestate at a 7.32 Hz rate. At about 4.37 seconds after the disablingswitch 303 is released, the Q7 output of binary counter 313 goes highenabling NAND gate 335 to pass the tone modulation output of NAND gate333 to MOSFET 339 via NAND inverter 337. The first time that the MOSFET339 turns on it fires the flashbulb 345. The flashbulb filamentvaporizes in microseconds so that the LC network (inductor 341,transducer 311 and capacitor 335) can be driven by MOSFET 339 almostimmediately. Since the flashbulb 345 element is in series, thevaporization of the flash element creates an open circuit between thebattery 305 and the start switch 301. This open circuit prevents thegrenade 100 from being reused until the flashbulb 345 has been replaced.Thus preventing unauthorized and unfair use of the "spent" trainingdevice.

The tone modulation signal continues for a period of about 4.37 seconds.At the end of this time interval, the Q8 output of the second binarycounter 313 goes high, resetting the first binary counter 307. When thefirst binary counter 307 resets, the oscillator portion of it is turnedoff so that the timer stops. Since the oscillator has stopped, Q8 of thesecond binary counter 313 remains high until the grenade pull pin isreinserted into the grenade 100, turning off power to the circuitry.When the timer and oscillator stop, the quiescent current drain on thebattery 305 falls to a level determined by the leakage currents of theCMOS integrated circuits, the leakage currents of capacitor 317 and 321and the current through resistor 347 and 349 (which are present todischarge capacitor 321 after the pull pin is reinserted into thegrenade 100). The typical quiescent current drain is about 45microamperes (9V/200K).

FIG. 3 shows a schematic of the receiver or MILES interface circuitrywhich comprises a quad operational amplifier (LMC 660) 200, a phase lockloop (LM 567) 202, a timer circuit (MC 1455G) 204, a microphone 200 andvarious discrete components. A rechargeable power section 201 providesvoltage to the applicable circuitry. All of the functions performed bythe receiver circuitry are accomplished using conventional, off theshelf, components with values shown as merely exemplary of anoperational device.

When an acoustic signal is received from an acoustic training device,such as the grenade previously described, the signal is detected by themicrophone 206. A conventional hearing aid may be used as the microphone206. The output of the microphone 206 is fed to the quad amplifier 200.The quad amplifier 200 is configured as two cascaded bandpass filtersfollowed by an active high pass filter. The filters are frequencyadjusted to center around the emitting frequency of the acoustictraining device and to amplify the microphone output. The output (pin 8)of the quad amplifier 200 is fed to the input (pin 3) of phase lock loopThe phase lock loop 202 is configured as a narrow band tone detector.The output (pin 8) of the phase lock loop 202 goes low when a signal ofthe proper frequency is presented to the input (pin 3) of the phase lockloop 202. The output (pin 8) of the phase lock loop going low causes thebase on transistor 208 to go low which allows capacitor 210 to charge.If the output (pin 8) of the phase lock loop 202 stays low long enoughfor capacitor 210 to charge beyond a set threshold, power supplied (bypin 3) to the MILES through timer 204 is removed. The MILES is thussupplied power through the output of timer 204 in place of the normalbattery in the MILES. Power remains removed from the MILES until theacoustic signal is no longer received from the acoustic training device.When the acoustic signal is no longer being received power is restoredto the MILES and its internal audible alarm is activated indicating a"hit" has taken place. Recall that the audible alarm is activated if thepower to the MILES is momentarily removed and then reconnected.

Another embodiment of the present invention is shown in FIG. 4 andincludes an additional phase lock loop 212. An additional phase lockloop provides for receiving coded pulse modulated signals transmittedfrom the acoustic training device. Only that portion of the circuitcentered around the additional circuitry is shown. The remaining portionis identical as provided in FIG. 3.

The circuitry preceeding the input (pin 5) of phase lock loop 202remains the same as shown in FIG. 3. The input signal comes from thequad amplifier 200. The output (pin 8) of phase lock loop 202 goes highand low at the pulse modulation Pate of the acoustic training device. Asecond phase lock loop 212 is inserted between phase lock loop 202 andtransistor 208 and acts as a tone decoder that only locks on to a signalat the modulation frequency. The output (pin 8) of phase lock loop 212goes low when an acoustic signal of the right frequency and modulationrate is received. The remaining portion of the circuit is identical andoperates as that shown in FIG. 3.

Obviously, numerous modifications and variations of the presentinvention ape possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. An acoustic training device for simulating theeffects of an omnidirectional weapon in a tactical engagement simulationsystem employing acoustic receivers, said training device comprising:ahousing which resembles in size and shape the weapon to be simulated;means disposed within said housing for generating an audible carriersignal of a particular frequency and duration; means to modulate saidaudible carrier signal at a predetermined frequency, wherein saidmodulated signal is of sufficient amplitude to be detected by anacoustic receiver only within a range corresponding substantially to thekill-zone of the weapon to be simulated, and the duration of said signalis such that it can be distinguished from transient signals and noise;means responsive to some external stimulus for activating said signalgenerating and modulating means.
 2. An acoustic training device forsimulating the effects of an omnidirectional weapon in a tacticalengagement simulation system employing acoustic receivers, said trainingdevice comprising:a housing which resembles in size and shape the weaponto be simulated; means disposed within said housing for generating anaudible carrier signal of a particular frequency and duration; means tomodulate said audible carrier signal at a predetermined frequency,wherein said modulated signal is of sufficient amplitude to be detectedby an acoustic receiver only within a range corresponding substantiallyto the kill-zone of the weapon to be simulated, and the duration of saidsignal is such that at least three modulations of said carrier signalare emitted so that the pulse-modulated signal can be distinguished fromtransient acoustic signals and noise; means responsive to some externalstimulus for activating said signal generating and modulating means. 3.An acoustic training device for simulating the effects of anomnidirectional weapon in a tactical engagement simulation systememploying acoustic receivers, said training device comprising:a housingwhich resembles in size and shape the weapon to be simulated; meansdisposed within said housing for generating an audible carrier signal ofa particular frequency and duration; means to modulate said audiblecarrier signal at a predetermined frequency, wherein the peak amplitudeof said modulated signal is approximately 80 dB at one meter, and theduration of said signal is such that at least three modulations of saidcarrier signal are emitted so that said modulated audible carrier signalcan be easily distinguished from transient signals and noise; meansresponsive to some external stimulus for activating said signalgenerating and modulating means.
 4. An acoustic training device forsimulating the effects of an omnidirectional weapon in a tacticalengagement simulation system employing acoustic receivers, said trainingdevice comprising:a housing which resembles in size and shape the weaponto be simulated; means disposed within said housing for generating anaudible carrier signal of a particular frequency and duration; means tomodulate said audible carrier signal so as to produce a pulse-modulatedsignal having a period of between 50 and 100 milliseconds, wherein thepeak amplitude of said modulated signal is approximately 80 dB at onemeter, and the duration of said signal is 1-5 seconds so that at leastthree modulations of said carrier signal are emitted allowing thepulse-modulated signal to be easily distinguished from transient signalsand noise; means responsive to some external stimulus for activatingsaid signal generating and modulating means.
 5. The invention of any oneof claims 1-4 wherein said audible signal generating and modulatingmeans comprises a power source, timing means, and an acoustic transducerresponsive to the output of said timing means, said timing meanscomprising two binary counters, the first of which provides asingle-frequency fundamental carrier signal to said transducer, and thesecond of which provides a tone modulation signal of a differentfrequency and on/off control signals to said transducer.
 6. Theinvention of claim 5 further comprising a plurality of NAND gates tologically combine said carrier frequency signal, tone modulationfrequency signal, and on/off control signals into a singlepulse-modulated signal of a particular duration.